Laura Robson, not yet out of her teenage years and soon to lose her wisdom teeth, has the consolation of time to soothe the disappointment of losing to Li Na in the third round of the US Open – 12 months after beating the Chinese player at the same stage of the tournament.

The British No1 and 30th seed here was a level or two below her best – certainly she did not hit the heights she reached in the first two rounds – and Li, 12 years older with a slam title to her name, looked determined to repair the hurt of 2012 as she ground out a 6-2, 7-5 win in a helter-skelter match that lasted only an hour and 21 minutes.

"I set my expectations quite high, so for me it's still quite disappointing," Robson said. "I thought I could have played a lot better today, but I always knew it was going to be a tough match. All in all, I guess it was an average week.

"I'm a more confident player. In my first two rounds I thought I closed out the matches really well, which is something that has improved a lot over the last 12 months. I think I'm going in the right direction. I feel like I'm improving and working on a more all-round game. It's going to take a lot of hard work, but I'm willing to do that. She was returning really deep. There wasn't a lot I could do in some points."

Physically, she has a couple of issues: her injured right wrist, which she taped heavily again, and her teeth.

"[I will take] a rest just so it settles down completely," she said of the wrist problem that has plagued her in recent weeks, "and I will see my doctor when I get back. I have to get my wisdom teeth taken out, as well. I have no idea how long I will be out. Jamie Hampton was trying to scare me. She was like: 'Oh, I couldn't do anything for three weeks'. I don't really listen to her, so ... hopefully just a couple of days."

It was Robson's old enemies – her feet – that got in her way in a sluggardly start, as she racked up a dozen unforced errors during the first quarter of an hour, handing an easy start to her clinical opponent.

Li dashed to a 5-1 lead after only 22 minutes and the match was sliding away from Robson at an alarming rate. She needed some equilibrium, some calm in the exchanges, so she could regroup and get into the match.

There were only a smattering of mid-morning fans on the vast main court of the complex and the echoes of support for Robson gave the match the feel of a low-key affair in the provinces – although she said it made no impact on her performance.

Her serve, which has improved markedly since she took on Miles Maclagan as coach, refused to click, but she found a good one into the corner to stay in the set. Li held, banging in her fourth and fifth aces to emphasise her dominance.

Sitting disconsolately and motionless in her chair at the changeover, Robson looked lost. Her right wrist taped, she might have been wondering if she had the two-fisted power to ask Li some difficult questions in the second set.

If she were to make a contest out of a hiding, she needed to break Li early. A cracking cross-court forehand for 15-30 on the Chinese player's serve was heartening, and then she grabbed her two break points, her first of the match. Li saved the first with her sixth ace, then hit long, and Robson's mood lifted.

Just as Robson was beginning to find her game, Li held with her seventh and eighth aces. Where Robson was still vulnerable was on her backhand, and she butchered a volley on a rare visit to the net and hit another long from deep. An overcooked forehand signalled a dip, and another one cost her the serve.

Serving to stay in the set, Li hit her 10th ace (to none), ramming home the impression that she was playing with the greater energy and buzz.

Serving at 5-5, Robson's backhand let her down again for break point, and a sloppy forehand gifted Li the chance to serve for a place in the last 16.

Robson kept her tournament alive with a blazing, hit-and-hope forehand that kissed the line for 30-15, and she forced a backhand error from Li for 30-30. But Robson could not handle yet another howitzer serve that brought the Chinese player her first match point. She blew it going for a forehand down the line, and Robson had scrambled to deuce.

On her second match point, however, Li hit her 11th ace, a fitting conclusion to a match in which she was in command for all but a few passages of play.

In the men's doubles, Britain's Jonny Marray and Colin Fleming beat Ryan Harrison of the United States and the Swede Robert Lindstedt, 6-3, 6-4, to reach the third round.